Process for producing pyridine carboxylic acids

ABSTRACT

A PROCESS FOR PRODUCING PYRIDINE CARBOXYLIC ACIDS BY OXIDIZLING ALKYL PYRIDINES IN THE LIQUID PHASE WITH A MOLECULAR OXYGEN-CONTAINING GAS IN THE PRESENCE OF A CATALYST CONSISTING OF ZIRCONIUM COMPOUNDS, SALTS OF OTHER TRANSITION METALS AND BROMINE COMPOUNDS.

United States Patent 3,801,584 PROCESS FOR PRODUCING PYRIDINE CARBOXYLIC ACIDS i Masayoshi Kubo and Takeshi Horikawa, Ohimachi,

Japan, assignors to Daicel Ltd., Osaka, Japan N0 Drawing. Filed'Dec. 27, 1971, Ser. No. 212,676 Claims priority, application Japan, Dec. 30,1970,

46/122,247 Int. Cl. C07d 31/34 US. Cl. 260-295 4 ABSTRACT OF THE DISCLOSURE A process for producing pyridine carboxylic acids by oxidizing alkyl pyridines in the liquid phase with a molecular oxygen-containing gas in the presence of a catalyst consisting of zirconium compounds, salts of other transition metals and bromine compounds.

gen-containing gas, there has been known only a process in which the alkyl pyridines in the liquid phase 1s oxidized acid is the most preferred. The amount of solvent to be used is preferably 2-6 times by weight, based on the weight of alkyl pyridines, and more preferably, 3-5 times by W ht-1' 1 I The reaction pressure should be sufficient to-keep the system in jthej liquid phase, and preferably it is in the range "kg/cm Reaction temperatures of higher than 17010. are required for effecting oxidation with a high conversion, and a temperature in the range of 200250 C. is particularly preferred.

As'the alkyl pyridine starting material to be used in this invention, although pyridine compounds having an aliphatic hydrocarbon radical substituted at the a-position are undesirable, other alkyl pyridines having any number of carbonatoms in the alkyl group may be used without limitatiom'for example, there may be employed fl-picoline,

"y-picoline, 3,4 lutidine, 3,5 lutidine, 3 ethyl pyridine,

by air in the presence of a catalyst consisting of bromine compounds and heavy metal salts (Japanese patent publication No. 9,868/1959 and French Pat. No. 1,185,919). According to Japanese patent publication No. 9,868/ 1959, however, the conversion is only 61.3% when the starting compound is ,B-picoline which has the highest reactivity, and with other alkyl pyridines, such as 'ypicoline, the conversion and the selectivity are even lower. When the concentration of alkylpyridines in the reaction system is increased, the conversion is sharply reduced thereby to decrease the reactivity greatly. The conversion is so low that a process for" recovering the expensive alkyl pyridines efiiciently is required in industrial production. However, as alkyl pyridines generally have high boiling points, the recovery ratio is not very high because of oxidation and decomposition on recovery by distillation, and the quality of the product, nicotinic acid, is also affected greatly. Because the conversion of alkyl pyridines to nicotinic acid is so low, there are many economic disadvantages, such as low production rate and high equipment cost.

It is, consequently, most important to increase the conversion to as high a level as possible on oxidizing alkyl pyridines, which has generally a low reactivity in the liquid phase.

SUMMARY OF THE INVENTION It has been discovered that, according to this invention, the conversion of alkyl pyridine to nicotinic acid can be increased greatly by using a catalyst system consisting of zirconium compounds, bromine compounds and soluble salts of transition metals, without reduction of the selectivity, resulting advantageously in a substantial reduction of the production cost.

The invention is explained more precisely in the following. The solvent to be used for the liquid phase reaction of this invention is not critical, provided that the solvent is inert in the oxidation condition and that it can dissolve the catalyst system of this invention. Lower saturated fatty acids are particularly preferred, and above all, acetic 4-e thylpy'ridine, 3-propyl pyridine, and 4-propyl pyridine. Thus, the pyridine compound has the formula wherein R R 1 and R is H, or an alkyl having 1 to 3 carbon atoms and at least one of R R and R is said alkyl.

As the catalyst, zirconium compounds, bromine compounds and salts of transition metals more or less show catalytic activity when used alone or as a combination of two components, but a remarkable increase of the catalytic activity is observed when there is used a mixed systemKof these three components, according to this invention.'All zirconium compounds that dissolve in the solvent :show' the catalytic effect, irrespective of the kinds of the anion present. As suitable zirconium compounds there may be exemplified zirconyl acetate, zirconium v nitrate, zirconium acetylacetonate, zirconium oxide, zirpresent in the initial-stage of the reaction. Although there is no particular limit as to the salts of transition metals, it

is preferable to employ either cobalt acetate or manganese acetate or both of-them simultaneouslysAs to the bromine compounds there is no particular limit except that they must be soluble in the solvent, and there may be exem plified ammonium bromide, hydrogen bromide, bromine,

cobalt bromide, manganese bromide, zirconium bromide, dibromoetliane, tetrabromoethane, and benzyl bromide; As described previously, "mixtures of zirconium compounds, bromine compounds and salts of transition metals generally show a remarkable catalytic activity, and above all, a combination of a zirconium compound with cobalt acetate, manganese acetate and ammonium bromide is par ticularly preferred. The amount of each catalyst component to be used is preferably about 0.1l0% by weight, based on the weight of the alkyl pyridine starting material, more preferably 0.52.0% by weight.

It has been observed that the zirconium compound-containing catalyst to be used according to this invention does not show any adverse effect on the quality of the product, and that the catalyst is effective for the air oxidation of the starting material in liquid phase.

Some illustrative examples of the invention are described below, but they do not limit the scope of the present invention.

a pressure below 20 kg./c1n. under the reaction system conditions of a temperature of 200 C. and a pressure of 20 kg./cm. As soon as the air was blown in, an exothermic reaction and oxygen absorption began. The reaction system reached at a maximum temperature of 230 C. after 30 minutes. The oxygen absorption .was the highest 30 minutes after the reaction began, and oxygen absorption stopped after one further hour. After 30 additional minutes the reaction was completed. The 3 total reaction time was only 2 hours. After the termination of the reaction, the crude reaction solution was separated into a solid and a filtrate. The solid was waterwashed and dried to obtain 139 parts of nicotinic acid. The filtrate was condensed and 58.3 parts of nicotinic acid were obtained as a residue. From the distillate 6 parts of p-picoline were collected. The conversion of ,8- picoline was 95 mol percent; the selectivity of nicotinic acid was 85 mol percent, and the yield of nicotinic acid was 80 mol percent. Nicotinic acid was recrystallized from water to produce a product of high purity having the melting point of 235-236 C. In the case of the same procedure as mentioned above, except that no zirconyl acetate was used, the conversion of p-picoline was 76% and the selectivity of nicotinic acid based on the converted p-picoline was 85%.

EXAMPLE 2 Oxidation of 'y-picoline was performed in the same way as described in Example 1. When zirconyl acetate was added, there were obtained a conversion of 'y-picoline of i 40 mol percent, a selectivity of iso-nicotinic acid of 80 mol percent, but when no zirconyl acetate was added, the conversion of 'y-picoline was 17 mol percent and the selectivity of iso-nicotinic acid was 80 mol.

EXAMPLE. 3

-.The same operation as described in Example 1 was carried out and the anion of the zirconium compound was varied. The results are-shown. in the following table.

Molpercent 1 Selectivity Yield of Time Conversion of nicotinic I nicotinic No. Zr compound (hr.) oIB-plcoline aci acid 1-- ZrO(OA): 2 94.1 i 85.0 80.0 2.- Zr(NO3)4 2 93. 95.0 79.1 3-. Zr(OsH1O:|)| 2 92.0 85.0 78. 4.. a 2 80.6 85.0 V 68.

Other components common to all the catalysts cobalt acetate tetrahydrate manganese acetate I ammonium bromide.

Inthe examples, all references to parts refer to parts by weight.

The embodiments of the invention, in which an exclusive property or privilege is claimed, are defined as follows:

1. A process for producing pyridine carboxylic acid which comprises oxidizing (1) alkyl pyridine of the formula wherein R R and R is H or alkyl of 1 to 3 carbon atoms, and at least one of R R and R is said alkyl, with (2) molecular oxygen or a molecular oxygen containing gas, in the liquid phase, at a temperature above about 17 C., in the presence of (3) a catalyst consisting essentially of (a) zirconium compound, (b) bromine or a bromine compound and (c) soluble salt of transition metal, the amounts of catalyst ingredients (a), (b) and (0) each being in the range of from 0.1 to 10% by weight, based on the weight of alkyl pyridine, during the oxidation.

2. A process according to claim 1, in which the reaction temperature is in the range of 200 to 250 C.

3. A process according to claim 1, in which the salt of transition metal is selected from the group consisting of cobalt acetate, manganese acetate and mixtures thereof.

4. A process according to claim 1, in which the alkyl pyridine is dissolved in an inert solvent, with the amount of the solvent being in the range of from 2 to 6 times the weight of the alkyl pyridine.

References Cited UNITED STATES PATENTS 3,012,038 12/1961 ONeil 260-295 R HENRY R. JILES, Primary Examiner A. M. CROWDER, Assistant Examiner US. 01. X.R. 260-2955 3 8 01 584 Dated April 2, 1974 Patent No.

Inventofls) Masavoshi Kubo and Takeshi Horikawa is certified that error appears in the above-identified paten ted as shown below "by correc and that said Letters Patent are here line 30'; change "17 C." to ---l70 C.-.

Signed andsealed this 10th day of September 1974.

MCCOY GIBSON 'JR. MARSHALL DANN Attestlng Officer Commissioner of Patents USCOMM'DC 5Q376-P69 U.S. GOVERflMENT PRINTING OFFICE: 963 0-366-32, 

